Shoulder prosthesis with variable inclination humeral head component

ABSTRACT

Methods and devices are disclosed for joint (e.g., shoulder) arthroplasty. In one aspect, there is provided a device for determining inclination and/or version of a prosthetic head with respect to a prosthetic stem. In another aspect, there is provided a joint (e.g., shoulder) prosthesis. In another aspect, there is provided a method for setting an inclination angle and/or a version angle of a prosthetic head with respect to a stem implanted or to be implanted in a bone of a joint (e.g., shoulder).

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/773,605, filed Sep. 8, 2015, now U.S. Pat. No. 10,226,349, and titledSHOULDER PROSTHESIS WITH VARIABLE INCLINATION HUMERAL HEAD COMPONENT,which is the § 371 U.S. National Stage Application of InternationalApplication No. PCT/US2014/020308, titled SHOULDER PROSTHESIS WITHVARIABLE INCLINATION HUMERAL HEAD COMPONENT, filed Mar. 4, 2014, whichclaims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional PatentApplication No. 61/774,969, filed on Mar. 8, 2013 and titled SHOULDERPROSTHESIS WITH VARIABLE INCLINATION HUMERAL HEAD COMPONENT, which arehereby incorporated by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a prosthesis and method for variableinclination and/or version of the humeral head component for shoulderarthroplasty, glenosphere for the shoulder, radial head for the elbow,or femoral head for hip arthroplasty.

2. Description of the Related Art

Various prostheses for the replacement of the shoulder joint are known.In one example shoulder prosthesis, the upper portion of the humerus isreplaced by a humeral component including (i) a stem, or cleat, thatextends into a bore formed within the humerus and (ii) a generallyhemispherical head portion that is connected to the stem. Thehemispherical head of the humeral component articulates with acomplementary concave section of a glenoid component mounted within theglenoid cavity of the scapula. This type of shoulder prosthesis may becalled a “primary” or “total” prosthesis. In another example shoulderprosthesis, often called a hemiarthroplasty, a hemispherical head of thehumeral component articulates with the native glenoid. In anotherexample shoulder prosthesis, often called a “reverse” or “inverted”prosthesis, the glenoid component includes a convex section thatarticulates with a complementary concave section of the head of thehumeral component.

There has been demonstrated to be a significant theoretical as well aspractical need to have variable inclination of the humeral component inshoulder arthroplasty. This has been demonstrated in strong marketplaceacceptance as well as a clear demand for this feature in shoulderarthroplasty. Elbow and hip arthroplasty shares a similar need forvariable adjustments. In addition, there is a future trend towardpatient specific instrumentation in shoulder, elbow, and hiparthroplasty. Variable inclination would be a very desirable, if notnecessary, component of any shoulder arthroplasty system to allow thesurgeon to exactly match the inclination chosen for the humeral headcomponent on the pre-operative plan and to match the instrumentation forthat individual patient.

However, a review of competitive systems in the marketplace reveals thatthe range of inclination provided by these systems does not properlyaddress the range of humeral head component inclination encountered atthe time of shoulder arthroplasty. In addition, many of the rangesprovided by shoulder arthroplasty systems are not physiologic and mayresult in significant component malposition. The range of inclination incurrently available systems appears randomly chosen without a trueanatomic basis.

In addition to a lack of understanding of the proper range ofinclination necessary for a humeral component, the method to achievethis inclination has associated challenges. There are several potentialstrategies to change the inclination of the humerus available in themarketplace. Each of these methods has disadvantages.

One can manufacture a variety of humeral stems that have a fixed amountof inclination. However, this can result in a significant increase ininventory requiring multiple stem inclinations for a wide breadth ofstem diameters.

In one alternative method, a set screw can be used within the stem tolock in the inclination angle of the humeral component. This can makethe set screw the “weak link” in the design and could be problematicduring attempted removal.

In another alternative method, one can use a screw through a lateralopening in the humeral stem and into the humeral head component to fixthe amount of inclination. This can result in making humeral headcomponent removal impossible without removing the humeral stem. Thissystem may be used without the set screw; however, the manufacturerrecommends impacting the head and stem together prior to insertion inthe humerus. However, the lateral opening in the humeral stem remains,making removal of the humeral stem much more difficult if used withcement.

In yet another alternative method, complex assembly can be performedwith a locking mechanism connecting the humeral stem and humeral headcomponent requiring more than ten steps. This method also does not allowone to place the stem in the humeral canal independent of the humeralhead component. This decreases the ability to place sutures in therotator interval and may have an effect on stability and outcome.

Thus, there exists a need for an improved prosthesis and method thatprovide for variable inclination and/or version of the humeral headcomponent in shoulder arthroplasty, as well as a need for variability inelbow and hip arthroplasty.

SUMMARY OF THE INVENTION

The present invention addresses the foregoing needs by providingimproved methods and devices for joint (e.g., shoulder) arthroplasty.There is provided a joint (e.g., shoulder) prosthesis. There is alsoprovided a device for determining inclination and/or version of aprosthetic head with respect to a prosthetic stem. There is alsoprovided a method for setting an inclination angle and/or a versionangle of a prosthetic head with respect to a stem implanted or to beimplanted in a bone of a joint (e.g., shoulder).

In one aspect, the invention provides a joint prosthesis including astem dimensioned to be implanted in a first bone of a joint of asubject; a prosthetic head having an outer surface dimensioned forarticulation with an articular surface of a natural or artificial jointsurface of a second bone of the joint; an adapter dimensioned to beimpacted into a depression in an end surface of the prosthetic headopposite the outer surface of the prosthetic head thereby forming aninterference fit between the adapter and the depression; and a mountingstud having a first end and a second end wherein the first end isdimensioned for impaction into a socket in the adapter thereby formingan interference fit between the first end and the socket, and the secondend is dimensioned for insertion into an opening in the stem.

In one version of the joint prosthesis, the second end of the mountingstud is dimensioned for impaction into the opening in the stem therebyforming an interference fit between the second end and the stem.

In another version of the joint prosthesis, the first end of themounting stud includes a spherical surface. The spherical surface of thefirst end of the mounting stud can be rotated in the socket to setinclination and/or version of the head with respect to the stem beforeforming the interference fit between the first end of the mounting studand the socket.

In another version of the joint prosthesis, the second end of themounting stud includes an outer surface that tapers inward from anintermediate section to an outermost section of the second end of themounting stud.

In another version of the joint prosthesis, the mounting stud includescircumferential reference indicia at or adjacent a junction of thespherical surface of the first end of the mounting stud and the outersurface of the second end of the mounting stud.

In another version of the joint prosthesis, a longitudinal axis of thesecond end of the mounting stud forms an oblique angle with respect toan axis of the prosthetic head when the interference fit is formedbetween the first end and the socket.

In another version of the joint prosthesis, the socket of the adapter isoffset with respect to a central longitudinal axis of the adapter.

In another version of the joint prosthesis, the adapter has a circularouter surface and the depression has a circular inner surface such thatthe adapter can be rotated in the depression to set radial offset of thehead with respect to the stem before forming the interference fitbetween the adapter and the depression.

In another version of the joint prosthesis, the head includes at leastone first reference marking for alignment with a second reference markon the adapter.

The joint prosthesis is suitable for use in different joints. Forexample, the first bone may be the humerus, and the second bone may bethe scapula. The first bone may be the scapula, and the second bone maybe the humerus. The first bone may be the femur, and the second bone maybe the pelvis. The first bone may be the humerus, and the second bonemay be the radius.

In another aspect, the invention provides a device for determining aninclination and/or a version of a prosthetic head with respect to a stemwherein the inclination and/or the version are used when the prosthetichead is coupled to the stem. The prosthetic head has an outer surfacefor articulation with an articular surface of a natural or artificialjoint surface of a bone of a joint of a subject. The device can includea body having a well; and a joint element having a first end and asecond end wherein the first end Is positioned in the well, and thesecond end is movable between positions wherein a longitudinal axis ofthe second end is angled with respect to an axis of the body.

One version of the device includes a retainer having an openingextending between a first side and an opposed second side of theretainer wherein the retainer is arranged in the well, and the retaineris dimensioned for translation in the well. The first end of the jointelement is dimensioned to be positioned between the body and the firstside of the retainer such that the second end of the joint elementextends through and outwardly of the opening of the retainer, and thesecond end of the joint element is dimensioned to be movable betweenpositions where the longitudinal axis of the second end is angled withrespect to an axis of the opening of the retainer. The retainer can havean oblong shape with a pair of parallel sides.

Another version of the device includes a fastener movable between afirst position in which the fastener allows the retainer to translate inthe well and a second position in which the fastener preventstranslation of the retainer in the well. The fastener may be a screwthat when in the second position causes the first end of the jointelement to be immobilized between the body and the retainer.

In one version of the device, the first end of the joint elementincludes a spherical bearing surface, and the second end of the jointelement includes an outer diameter that decreases from an intermediatesection to an outermost section of the second end of the joint element.The second end of the joint element may be dimensioned to contact aninner surface of an opening in the stem.

In one version of the device, the body and the retainer includereference markings for determining a positional relationship of theretainer with respect to the body.

The device is suitable for determining an inclination and/or a versionof a prosthetic head with respect to a stem of a prosthesis fordifferent joints. For example, the prosthetic head may articulate withthe scapula when the joint is the shoulder. The prosthetic head mayarticulate with the humerus when the joint is the shoulder. Theprosthetic head may articulate with the pelvis when the joint is thehip. The prosthetic head may articulate with the radius when the jointis the elbow.

In another aspect, the invention provides a method for setting aninclination angle and/or a version angle of a prosthetic head withrespect to a stem implanted or to be implanted in a bone of a joint of asubject. The method uses a trial device including (i) a body having awell, and (ii) a joint element having a first end and a second endwherein the first end is positioned in the well, and the second end ismovable between positions wherein a longitudinal axis of the second endis angled with respect to an axis of the body. The second end of thejoint element is inserted in an opening in the stem, and the jointelement is immobilized with respect to the body. A mounting stud issecured to the prosthetic head in a fixed position with respect to theprosthetic head so as to match an orientation of the immobilized jointelement with respect to the body. An end of the mounting stud may besecured in the opening in the stem.

In one version of the method, the trial device further includes aretainer arranged in the well, and the first end of the joint elementmay be immobilized between the body and the retainer. The retainer maybe dimensioned for translation in the well, and the method may comprisepreventing translation of the retainer in the well. A fastener may bemovable into a position in which the fastener prevents translation ofthe retainer in the well.

In another version of the method, a template is placed over theimmobilized joint element, and a position of a reference line on thetemplate with respect to a first reference point on the body is noted.The template is then placed over the mounting stud, and the referenceline is aligned with a second reference point on the prosthetic head.The mounting stud is then secured to the prosthetic head in the fixedposition with respect to the prosthetic head. The template may includean opening, and the opening may be placed over the immobilized jointelement before noting the position of the reference line on the templatewith respect to the first reference point on the body. The opening maybe placed over the mounting stud before aligning the reference line withthe second reference point on the prosthetic head.

In another version of the method, the mounting stud can be moved to afirst angle with respect of the prosthetic head before the mounting studis secured to the prosthetic head in the fixed position. The first angleis about the same (e.g., ±20°, or ±10°, or ±5°) as a second angle of theimmobilized joint element with respect to the body. The first angle canbe determined using a first reference circle surrounding the mountingstud, and the second angle can be determined using a second referencecircle surrounding the joint element. The first angle can be determinedusing a first reference circle surrounding the mounting stud and areference line on the template, and the second angle can be determinedusing a second reference circle surrounding the joint element and thereference line on the template.

The method is suitable for setting an inclination angle and/or a versionangle of a prosthetic head with respect to a stem implanted or to beimplanted in a bone of various joints of a subject. The bone can be thescapula, and the joint can be the shoulder. The bone can be the humerus,and the joint can be the shoulder. The bone can be the femur, and thejoint can be the hip. The bone can be the humerus, and the joint can bethe elbow.

In one non-limiting embodiment, it is an advantage of the invention touse a humeral head assembly with a taper to set the inclination/versionof a shoulder prosthesis. This construct allows for the use of apre-existing stem design. The variable inclination is a part of thehumeral head assembly. The use of a taper within the humeral headassembly provides the ability to not only change humeral inclination butalso humeral version. This eliminates the need to create a separatehumeral stem to allow adjustment for inclination and version. A taper ofthe humeral head assembly has the ability to rotate and then lock inplace at the desired inclination/version in the humeral head. Thisallows the surgeon to maximize intraoperative flexibility by using onestem design to achieve the desired amount of inclination and version.This has the benefit of decreasing humeral component inventory andallows changing humeral inclination/version without removing the stem.

The proper range of inclination can be established with patient studiesin order to properly define the range of inclination that willaccommodate patients. This can facilitate the accurate and efficientdesign of a variable inclination system to determine the exact range ofinclination that is necessary for the system.

Adjustment of humeral inclination has become a clear need in theshoulder arthroplasty marketplace. Significant deficiencies have becomerecognized in the currently available systems including a range ofinclinations that are not based on the anatomic distribution. Moreover,the currently available systems used to create variable inclination havesignificant technical drawbacks. Therefore, the method of the inventionhas been designed to address these significant market needs. Inaddition, applications that may benefit from similar adjustabilityinclude the glenosphere of the shoulder, radial head of the elbow,femoral head of the hip, and the like.

These and other features, aspects, and advantages of the presentinvention will become better understood upon consideration of thefollowing detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional shoulder prosthesis.

FIG. 2 is an anterior view, partially in cross section, of oneembodiment of a shoulder prosthesis according to the invention.

FIG. 3 is a view of the shoulder prosthesis of FIG. 2, taken along line3-3 of FIG. 2.

FIG. 4 is a bottom view of a trial head assembly used in implanting ashoulder prosthesis according to the invention.

FIG. 5 shows a template and components of a humeral head assembly kit ofa shoulder prosthesis according to the invention.

FIG. 6 is a top perspective view of a step in assembling a humeral headassembly of a shoulder prosthesis according to the invention.

FIG. 7 is a top view of a step, subsequent to FIG. 6, in assembling ahumeral head assembly of a shoulder prosthesis according to theinvention.

FIG. 8 is a top perspective view of a step, subsequent to FIG. 7, inassembling a humeral head assembly of a shoulder prosthesis according tothe invention.

FIG. 9 is a top perspective view of a step, subsequent to FIG. 8, inassembling a humeral head assembly of a shoulder prosthesis according tothe invention.

Like reference numerals will be used to refer to like parts from Figureto Figure in the following description of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Looking first at FIG. 1, there is shown an example conventional shoulderprosthesis 10. The upper portion of the humerus 12 is replaced by ahumeral component 14 including a stem 16 that extends into a bore formedwithin the humerus 12. Typically, the stem 16 is fixed within the boreformed within the humerus 12. The stem 16 has a longitudinal stem axisS. A generally hemispherical head 18 is connected to the stem 16.Alternatively, the head 18 is integral with the stem 16. Thehemispherical head 18 has a base surface 19 and a longitudinal head axisH. The hemispherical head 18 of the humeral component 14 articulateswith a complementary concave section 22 of a glenoid component 24 thatis fixed within the glenoid cavity of the scapula 26 using cemented oruncemented posts 28. The glenoid component 24 includes a base surface 27opposite the concave section 22 that serves as an articular surface ofthe glenoid component 24.

Referring now to FIGS. 2-3, there is shown an example embodiment of ashoulder prosthesis according to the invention. The humeral component 34includes a stem 36 that extends into a bore formed within the humerus12. The stem 36 has a longitudinal stem axis S. A humeral head assembly37 has a generally hemispherical head 38. The humeral head assembly 37is connected to the stem 36. The outer surface 41 of the hemisphericalhead 38 of the humeral component 34 articulates with a complementaryconcave section 22 of a glenoid component 24 that is fixed within theglenoid cavity of the scapula 26 as shown in FIG. 1. In the humeral headassembly 37, the head 38 includes a depression 43 that receives anadapter 46 having a body 47 with a socket 48 that is eccentric, i.e.,the central axis of the socket 48 is offset from the central axis of thebody 47. The humeral head assembly 37 also includes a mounting stud 51having a first end 53 with a spherical bearing surface 54 and a secondend 56 comprising a tapered shaft 57. The first end 53 of the mountingstud 51 is secured in the socket 48 of the adapter body 47 by way of aninterference fit formed by impacting the mounting stud 51 in the socket48. The second end 56 of the mounting stud 51 is secured in a stemopening 61 of the stem 36 by way of a taper lock formed by impacting themounting stud 51 in the stem opening 61.

The parts of the humeral component 34 may be formed from, for example:(i) a metal or metal alloy such as a titanium alloy (e.g.,titanium-6-aluminum-4-vanadium), a cobalt alloy, a stainless steelalloy, or tantalum; (ii) a nonresorbable ceramic such as aluminum oxideor zirconia; (iii) a nonresorbable polymeric material such aspolyethylene; or (iv) a nonresorbable composite material such as acarbon fiber-reinforced polymers (e.g., polysulfone). The prostheticcomponent can be manufactured by machining an article formed from thesematerials, or by molding these materials in a suitable mold.

In FIG. 2, taking the included angle in an anterior view between stemaxis S and head axis H in degrees and subtracting from 180° is one wayto define the inclination angle A_(inclination) of the humeral head 38in degrees. The inclination angle of the humeral head 38 can be adjustedto have a selected angle between the longitudinal head axis H and thelongitudinal stem axis S by assembling the humeral head assembly 37 withthe socket 48 of the adapter body 47 in a selected position with respectto the head 38 and with the mounting stud 51 in a selected orientationin the socket 48 of the adapter body 47 as described below.

In FIG. 3, taking the included angle in a medial view between stem axisS and head axis H in degrees is one way to define the version angleA_(version) of the humeral head 38 in degrees. The version angle of thehumeral head 38 can be expressed as a positive or negative angle withrespect to the stem axis S. The version angle of the humeral head 38 canbe adjusted to have a selected positive or negative angle between thelongitudinal head axis H and the longitudinal stem axis S by assemblingthe humeral head assembly 37 with the socket 48 of the adapter body 47in a selected position with respect to the head 38 and with the mountingstud 51 in a selected orientation in the socket 48 of the adapter body47 as described below.

Referring now for FIGS. 4-9, a surgeon can implant the humeral component34 so that the humeral component 34 articulates with a complementaryconcave section 22 of a glenoid component 24. The fixing of the glenoidcomponent 24 within the glenoid cavity of the scapula 26 can be done ina conventional manner. A method of the invention uses a trial headassembly 63 (see FIG. 4). A trial head assembly 63 is prepared, and thenthe orientation of the adapter 46 and the mounting stud 51 of thehumeral head assembly 37 are matched to the trial head assembly 63.

The trial head assembly 63 includes a body 65. Looking at FIG. 4, oneside of the body 65 has an generally oblong shaped well 66 with offsetmarkings 67 (A,B,C,D,E) on parallel side sections of the well 66.Opposite the side of the body 65 having the well 66, there is a side ofthe body 65 that has a generally hemispherical surface identical orsubstantially similar to the outer surface 41 of the hemispherical head38 of the humeral component 34. A retainer 69 can slide in the well 66of the body 65 as shown at L in FIG. 4. In the trial head assembly 63,set screws 70 can lock the position of the retainer 69 in the well 66.The oblong shape of the well 66 may prevent the retainer 69 fromrotating within the well 66 while set screws 70 are tightened(similarly, pins, and the like, may be used that slide alongtightly-clearanced slots to prevent rotation of the retainer 69). Theretainer 69 has an opening 71, and cross hair markings 72. A ball jointelement 75 of the trial head assembly 63 has a first end 77 withspherical bearing surface 78 and a second end 79 in the shape of atapered shaft 80. The second end 79 of the ball joint element 75protrudes outwardly through the retainer opening 71, and the first end77 of the ball joint element 75 is positioned between the retainer 69and the surface of the well 66. When the set screws 70 are tightened,the second end 79 of the ball joint element 75 is secured by contactwith a surface of the retainer 69 and the surface of the well 66. Threeconcentric reference circles 81 surround the ball joint element 75 nearthe junction of the spherical bearing surface 78 and the tapered shaft80.

Shown in FIG. 5 is a transparent template 82 that can be used to matchthe orientation of the components of the humeral head assembly 37 andthe trial head assembly 63. The template 82 has an opening 83, referencelines 84, and cross hair markings 85. The template 82 may take otherforms, such as a platform with a non-marring, low-friction surface forthe head to rest upon while it is being rotated to its maximum offset,while still retaining an opening 83, and reference lines 84.

Preparing the trial head assembly 63 begins with ensuring that the twoset screws 70 on the trial head assembly 63 are loose. One verifies thatthe ball joint element 75 rotates freely in all directions and theretainer 69 slides freely in the well 66. The stem 36 is fixed within abore formed within the humerus 12 (see FIG. 2). The second end 79 of theball joint element 75 is then seated in the stem opening 61 of the stem36 which has been implanted in the humerus 12 of a patient. The body 65of the trial head assembly 63 is adjusted to the desired radial offset,inclination and/or version in the patient, and the two set screws 70 aretightened to lock the offset and the angle of the ball joint element 75of the trial head assembly 63. The set screws 70 are accessible on aside of the body 65 opposite the retainer 69. The trial head assembly 63is then removed from the stem 36.

The trial head assembly 63 is then turned upside-down such that theretainer 69 and the ball joint element 75 are visible to the surgeon asin FIG. 4. The surgeon notes the four cross-hair markings 72 on thesurface of the retainer 69, ninety degrees apart. The offset isindicated by the position of the vertical markings of the cross hairmarkings 72 of the retainer 69 relative to the A, B, C, D, and E offsetmarkings 67 on the body 65. The surgeon also notes a reference angleindicated by the concentric reference circles 81 on the ball jointelement 75. In the non-limiting example configuration shown, there arethree concentric reference circles 81 present on the ball joint element75, which can be of different colors such as black, red, and blue. Thereference angle is read by noting the position of the concentricreference circles 81 at the location where one of the cross-hairmarkings 72 would intersect the inner opening 71 circumference of theretainer 69. By noting the position of the concentric reference circles81 at two of these orthogonal locations (i.e., two adjacent cross-hairmarkings 72), the reference angle is fully characterized.

The humeral head assembly 37 is assembled to match the orientation ofthe ball joint element 75 in the trial head assembly 63. The adapter 46is Inserted into the head 38, and the adapter 46 is rotated so that theoffset reference markings 44 on the head 38 align with the appropriateoffset reference mark 49 on the adapter 46. See FIG. 6.

Still referring to FIG. 6, an impactor 88 is then used in the method ofthe invention. The impactor 88 has a round flat end surface 89, a firstside wall 90 with an end surface 91, and a second side wall 92 with anend surface 93. The end surfaces 91, 93 of the impactor 88 are placed ontop of adapter 46, and a mallet is used to strike the flat end surface89 of the impactor 88 to seat the adapter 46 inside the depression 43 ofthe head 38.

Looking at FIG. 7, the first end 53 of the mounting stud 51 is placedvertically onto the socket 48 of the adapter 46, and the mounting stud51 is pressed down using just enough force to barely seat it. The socket48 may also be lined with a material, such as rubber, that may act tohold the stud 51 in place. The opening 83 of the transparent template 82is placed over the second end 56 of the mounting stud 51, and thereference lines 84 of the template 82 are used to align the maximumoffset direction of the head 38 with the maximum offset direction of thebody 65 of the trial head assembly 63. The template 82 is removed,noting its position relative to the head 38. FIG. 7 shows how the trialhead assembly 63 can be located adjacent the humeral head assembly 37during assembly for reference.

Turning to FIG. 8, an impactor ring 95 having an aperture 96 is placedover the mounting stud 51, and rotated so the impactor ring 95 alignswith the indexing features of the adapter 46. As noted above, the stud51 should not change orientation during assembly, and the impactor ring95 may be lined with a material, such as rubber, to prevent motion. Theimpactor ring 95 is pushed into the pocket of the adapter 46. Thetemplate is re-placed over the mounting stud 51 in the same position aswhen the template 82 was removed. The cross-hair markings 85 on thetransparent template 82 are referenced, and the mounting stud 51 ismoved to the same angle of the ball joint element 75 of the trial headassembly 63 using concentric reference circles 59 which surround themounting stud 51 near the junction of the spherical bearing surface 54and the tapered shaft 57 of the mounting stud 51. The template 82 isthen removed.

Looking at FIG. 9, the angle of the mounting stud 51 of the head 38 andthe ball joint element 75 of the trial head assembly 63 are visuallycompared by looking at them horizontally from two orthogonal directions.If the angles match acceptably, one gently pushes down on the impactorring 95, applying even pressure around the mounting stud 51. Theimpactor ring 95 holds the mounting stud 51 at the correct angle duringthe subsequent steps. One then visually re-confirms that the angle ofthe mounting stud 51 of the humeral head assembly 37 is stillacceptable.

The impactor 88 is positioned concentric with the impactor ring 95 withthe end surfaces 91, 93 of the impactor 88 contacting the impactor ring95. One uses downward pressure to hold the impactor 88 in place with onehand, and then one strikes the end surface 89 of the impactor 88 with amallet. This pushes down the impactor ring 95, which in turn drives themounting stud 51 into an interference fit with the socket 48 of theadapter 46. The interference fit may be enhanced by modifying thesurfaces of either the mounting stud 51, or the socket 48, by abrasiveblasting, roughening the surfaces, cutting rough machining lines, oradding sharp blade-like structures to engage the opposing surface, andthe like, or otherwise modifying the shape of either the mounting stud51 or the socket 48. The mounting stud 51 is fully seated when the topsurface of the impactor ring 95 is approximately flush with the topsurface of the adapter 46. One then visually re-confirms that the angleof the mounting stud 51 of the humeral head assembly 37 is stillacceptable.

The impactor ring 95 can be removed by pinching two tabs 97 with thethumb and Index finger and pulling upward. The humeral head assembly 37is now ready for implantation. The second end 56 of the mounting stud 51of the humeral head assembly 37 is secured in a stem opening 61 of thestem 36. Seating the humeral head assembly 37 in the humeral stem 36using a mallet further seats the assembled components together as inFIG. 2.

Thus, the invention provides an improved prosthesis and method thatprovide for variable inclination and/or version and/or offset of thehumeral head component in shoulder arthroplasty. While a human cadavericvalidation has been done with respect to the methods and the shoulderarthroplasty components, the method could be used for other joints(e.g., hip, knee, elbow, foot, ankle, etc. . . . ).

Although the present invention has been described in detail withreference to certain embodiments, one skilled in the art will appreciatethat the present invention can be practiced by other than the describedembodiments, which have been presented for purposes of illustration andnot of limitation. Therefore, the scope of the appended claims shouldnot be limited to the description of the embodiments contained herein.

What is claimed is:
 1. A head assembly of a joint prosthesis, the headassembly comprising: a prosthetic head having an outer surfacedimensioned for articulation with an articular surface of a natural orartificial joint surface of a bone of a joint of a subject; an adapterdimensioned to be impacted into a depression in an end surface of theprosthetic head opposite the outer surface of the prosthetic headthereby forming an interference fit between the adapter and thedepression; and a mounting stud having a first end and a second end,wherein the second end is located distal from the first end along amounting stud axis extending through the first end and the second end ofthe mounting stud, the first end comprising a spherical surfacedimensioned for impaction into a socket in the adapter thereby formingan interference fit between the first end and the socket, wherein thefirst end of the mounting stud and the socket are configured to allowfor adjustment of an orientation of the prosthetic head relative to themounting stud axis over a range of inclination angles before forming theinterference fit, and wherein a selected inclination angle within therange of inclination angles is fixed by the interference fit between thefirst end of the mounting stud and the socket.
 2. The head assembly ofclaim 1 wherein the spherical surface of the first end of the mountingstud is configured to be rotated in the socket to set inclination and/orversion of the prosthetic head before forming the interference fitbetween the first end of the mounting stud and the socket.
 3. The headassembly of claim 1 wherein the second end of the mounting stud includesan outer surface that tapers inward towards the mounting stud axis froman intermediate section to an outermost section of the second end of themounting stud, the mounting stud including circumferential referenceindicia at or adjacent a junction of the spherical surface of the firstend of the mounting stud and the outer surface of the second end of themounting stud.
 4. The head assembly of claim 1 wherein the socket of theadapter is offset with respect to a central longitudinal axis of theadapter, wherein the adapter comprises a circular outer surface and thedepression comprises a circular inner surface such that the adapter isconfigured to be rotated in the depression to set a radial offset of theprosthetic head with respect to the socket of the adaptor before formingthe interference fit between the adapter and the depression, wherein theprosthetic head includes at least one first reference marking foralignment with a second reference mark on the adapter.
 5. The headassembly of claim 1, wherein the first end of the mounting stud and thesocket are configured to allow for adjustment of an orientation of theprosthetic head relative to the mounting stud such that a version angleof the prosthetic head relative to the mounting stud axis extendingthrough the mounting stud comprises a selected version angle within arange of version angles.
 6. The head assembly of claim 1, wherein thefirst end of the mounting stud comprises a modified spherical surfaceconfigured to enhance the interference fit between the first end and thesocket.
 7. The head assembly of claim 6, wherein the modified sphericalsurface comprises a roughened surface.
 8. The head assembly of claim 6,wherein the modified spherical surface comprises machining lines.
 9. Thehead assembly of claim 6, wherein the modified spherical surfacecomprises structures configured to engage an opposing surface of thesocket.
 10. The head assembly of claim 1, wherein the socket comprises amodified surface configured to enhance the interference fit between thefirst end of the mounting stud and the socket.
 11. The head assembly ofclaim 10, wherein the modified surface comprises a roughened surface.12. The head assembly of claim 10, wherein the modified surfacecomprises machining lines.
 13. The head assembly of claim 10, whereinthe modified surface comprises structures configured to engage anopposing surface of the first end of the mounting stud.
 14. The headassembly of claim 1, wherein the prosthetic head is attached to thefirst end of the mounting stud in the absence of a threaded fastener.15. A head assembly of a joint prosthesis, wherein the head assemblycomprises: a prosthetic head having an outer surface dimensioned forarticulation with an articular surface of a natural or artificial jointsurface of a bone of a joint of a subject; an adapter dimensioned to beimpacted into a depression in an end surface of the prosthetic headopposite the outer surface of the prosthetic head, thereby forming aninterference fit between the adapter and the depression; and a mountingstud having a first end and a second end, wherein the second end islocated distal from the first end along a mounting stud axis extendingthrough the first end and the second end of the mounting stud, the firstend dimensioned for impaction into a socket in the adapter therebyforming an interference fit between the first end and the socket,wherein the first end of the mounting stud comprises a modifiedspherical surface configured to enhance the interference fit between thefirst end and the socket; wherein the first end of the mounting stud andthe socket are configured to allow for adjustment of an orientation ofthe prosthetic head relative to the mounting stud axis extending throughthe mounting stud within a range of inclination angles, and wherein aselected inclination angle within the range of inclination angles isfixed by the interference fit between the first end of the mounting studand the socket, and wherein the first end of the mounting stud and thesocket are configured to allow for adjustment of an orientation of theprosthetic head relative to the mounting stud axis such that a versionangle of the prosthetic head on the mounting stud comprises a selectedversion angle within a range of version angles; and wherein the enhancedinterference fit between the modified spherical surface of the first endof the mounting stud and the socket alone retains the prosthetic head atthe selected inclination angle and the selected version angle afterimplantation and in the absence of a threaded fastener.
 16. The headassembly of claim 15, wherein the modified spherical surface comprises aroughened surface.
 17. The head assembly of claim 15, wherein themodified spherical surface comprises machining lines.
 18. The headassembly of claim 15, wherein the modified spherical surface comprisesstructures configured to engage an opposing surface of the socket. 19.The head assembly of claim 15, wherein the modified spherical surface ofthe first end of the mounting stud can be rotated in the socket to setinclination and/or version of the prosthetic head with respect to themounting stud axis before forming the interference fit between the firstend of the mounting stud and the socket.
 20. The head assembly of claim15, wherein the second end of the mounting stud includes an outersurface that tapers inward towards the mounting stud axis from anintermediate section to an outermost section of the second end of themounting stud, the mounting stud including circumferential referenceindicia at or adjacent a junction of the modified spherical surface ofthe first end of the mounting stud and the outer surface of the secondend of the mounting stud.
 21. The head assembly of claim 15, wherein thesocket of the adapter is offset with respect to a central longitudinalaxis of the adapter, wherein the adapter has a circular outer surfaceand the depression has a circular inner surface such that the adaptercan be rotated in the depression to set a radial offset of theprosthetic head with respect to the socket of the adaptor before formingthe interference fit between the adapter and the depression, wherein theprosthetic head includes at least one first reference marking foralignment with a second reference mark on the adapter.